Does subsurface drainage remove plant-available water from the soil?
No, drainage does not increase or decrease plant- available water in the soil profile. Drainage removes “drainable” water from the soil the same way a potted plant with a hole in the bottom of the pot drains after watering. Upward flow can occur in soil with tile drains, however, from the water table to the root zone, providing an important source of moisture for crop growth. On lighter (coarser) soils, placing drains too deep can limit this source of moisture. Is groundwater or rainfall the source of subsurface drainage water? In most situations, flow from drainage systems is shallow groundwater that is replenished by rainfall-the less rainfall there is, the less drainage flow there can be. In some cases, however, drainage systems are designed to intercept lateral flow. Does subsurface drainage cause more water to leave the field compared to undrained conditions? While not true for all cases and locations, in general, subsurface drainage may cause 10 to 15 percent more water to leave
